A nonaqueous electrolyte battery using titanium oxide as the negative electrode enables stable and rapid charge/discharge and also has a longer life than a battery using a carbon type negative electrode. However, titanium oxide has a higher potential with respect to metal lithium than carbonaceous materials. Also, titanium oxide has a low capacity per weight. Therefore, a battery using titanium oxide as the negative electrode has a low energy density.
The theoretical capacity of titanium dioxide having an anatase structure is about 165 mAh/g and that of a lithium-titanium composite oxide having a spinel structure, such as Li4Ti5O12, is about 170 mAh/g. On the other hand, the theoretical capacity of a graphite type electrode material is 385 mAh/g or more. The capacitance density of titanium oxide is significantly lower than that of a carbon type negative electrode material as mentioned above. This is due to reduction in substantial capacity because the number of lithium absorbing sites is small in the crystal structure of titanium oxide and lithium tends to be stabilized in the structure.
In light of this, a titanium oxide compound having the crystal structure of a monoclinic titanium dioxide has recently attracted attention. Monoclinic titanium dioxide can release/absorb a maximum of 1.0 of lithium ion per one titanium ion, and therefore, a titanium dioxide compound having the crystal structure of monoclinic titanium dioxide has a theoretical capacity of about 330 mAh/g, which is significantly higher than those of other titanium oxide compounds.
However, when a titanium oxide compound having the crystal structure of monoclinic titanium dioxide is used as an electrode material, the performance of a battery is significantly deteriorated, giving rise to the problem as to reduced the cycle life.